There are few truly non-invasive tests available to measure left ventricular diastolic function in patients with cardiac disease. In this study we utilized pulsed Doppler to assess transmitral flow-velocity patterns and characterize left ventricular filling and relaxation in 109 patients with hypertrophic cardiomyopathy and 86 normal controls. All Doppler indexes of diastolic function in patients with hypertrophic cardiomyopathy differed significantly from those in 86 control subjects without heart disease of similar ages (p less than 0.001): duration of isovolumic relaxation (94.2 plus/minus 24 versus 77.6 plus/minus 12 ms) and duration of the early diastolic peak of flow-velocity (245 plus/minus 54 versus 220 plus/minus 28 ms) were both prolonged and the rate of decrease (descent) of flow-velocity in early diastole diastolic filling velocity was reduced (3.4 plus/minus 1.4 versus 4.9 plus/minus 1.4 m/sec2); as an apparent compensation for impaired relaxation and early diastolic filling, the atrial contribution to left ventricular filling was increased, as shown by the reduced ratio between the heights of the early and late (atrial) peaks of flow-velocity (1.5 plus/minus 0.8 versus 2.1 plus/minus 0.9). The vast majority of patients with hypertrophic cardiomyopathy showed evidence of impaired left ventricular diastolic function based on alterations in the Doppler waveform (-- of 109 patients, or 77%). Diastolic dysfunction was identified with similar frequency in patients without left ventricular outflow obstruction (78%) or with obstruction (70%), as well as in asymptomatic (73%) or symptomatic patients (82%). These findings demonstrate that pulsed Doppler echocardiography may be used to quantitatively assess left ventricular function and that impairment in left ventricular filling and relaxation are common and clinically important abnormalities in a population of patients with hypertrophic cardiomyopathy.